Mechanism of Ca<SUP>2+</SUP> influx by extracellular ATP in NG 108-15 cells

• ISHIMOTO Hiromi

  Department of Pharmacology, Fukushima Medical College

• KIMURA Junko

  Department of Pharmacology, Fukushima Medical College

• MATSUOKA Isao

  Department of Pharmacology, Fukushima Medical College

• KUMASAKA Tadanori

  Department of Pharmacology, Fukushima Medical College

• NAKANISHI Hironori

  Department of Pharmacology, Fukushima Medical College

Bibliographic Information

Other Title

• NG108-15細胞のATPにより誘発される非選択性陽イオン電流

Abstract

ATP at 100 μM induced a trasient [Ca²⁺]_i increase, while at 1 mM it induced the transient increase followed by a sustained [Ca²⁺]_i increase in NG108-15 cells. We examined the mechanism of this sustained [Ca²⁺] increase using the fura-2 fluorescent method and the whole-cell patch clamp technique. Pretreatment of the cells with U73122 (PLC inhibtor) completely inhibited the trasient [Ca²⁺]_i increase but not the sustained [Ca²⁺]_i increase by ATP. The sustained [Ca²⁺]_i increase was not observed in the absence of extracellular Ca²⁺, suggesting that this component was due to Ca²⁺ influx. Under the whol-cell patch clamp, 1 mM ATP induced a membrane current with the reversal potential at 12.5±0.8 mV in Tyrode solution with the Cs⁺ aspartate pipete solution. The ATP-induced current increased in a concentration dependent manner with EC₅₀ value of approximately 0.75 mM ATP. When external Na⁺ was replaced by Li⁺, K⁺, Rb⁺, Cs⁺ or NMG⁺, ATP induced the current with a slight shift in the reversal potentials, suggesting that ATP activated a nonselective cation current. From the reversal potentials, the permeability ratio was calculated to be Na⁺ (1) > Li⁺ (0.93) > K⁺ (0.89) > Rb⁺ (0.56) > Cs⁺ (0.47) > NMG⁺ (0.12). Upon total replacement of external cation with Ca²⁺, ATP could induce the current, inicating that Ca²⁺ was permeable through the current. The permeability ratio of Ca²⁺ : Na⁺ was 1 : 0.6. ATP analogues which induced the current were 2MeSATP, BzATP, ATPγs and ADPβs. UTP had only a small effect and adenosine did not induce any current. α, β MetATP, β, γMetATP and ADP induced a different type of current. In fura-2 fluorescent method, ATPγs increased [Ca²⁺]_i sustaindly but α, β MetATP and β, γ MetATP did not do so. These results indicated that ATP induced a nonselective cation current via P_2Z receptor subtype. ATP-induced current was larger at lower [Mg²⁺]_o, indicating that ATP^4- was an effective agonist form of ATP. Calculated EC₅₀ value was 21.5 μM ATP^4-. We conclude that a high concentration of ATP stimulates P_2Z receptor which is coupled to a class of Ca²⁺-permeable nonselective cation channels through which Ca²⁺ influx occurs in NG 10815 cells.

Journal

• Folia Pharmacologica Japonica

  Folia Pharmacologica Japonica 106 (supplement), 138-142, 1995

  The Japanese Pharmacological Society

Keywords

• Pharmacology

Details

• CRID: 1390001204270928000
• NII Article ID: 10008631373
• NII Book ID: AN00198335
• DOI: 10.1254/fpj.106.supplement_138
• ISSN: 13478397
• ISSN: 00155691
• Text Lang: ja
• Data Source:
  • JaLC
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed